OFFSET
1,2
COMMENTS
Obviously there can be no even terms in this sequence. - Alonso del Arte, Jun 18 2017
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000 (terms 1..1740 from Vincenzo Librandi)
EXAMPLE
Concatenate 4 and 1 to get 41, which is prime, so 1 is in the sequence.
Concatenate 4 and 3 to get 43, which is prime, so 3 is in the sequence.
Concatenate 4 and 5 to get 45 = 3^2 * 5, which is not prime, so 5 is not in the sequence.
MATHEMATICA
Select[2Range[250] - 1, PrimeQ[FromDigits[Join[{4}, IntegerDigits[#]]]] &] (* Alonso del Arte, Jun 18 2017 *)
PROG
(PARI) isok(n) = isprime(eval(concat(4, Str(n)))); \\ Michel Marcus, Jun 19 2017
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, May 15 1998
EXTENSIONS
Offset adjusted at the suggestion of Michel Marcus by Alonso del Arte, Jun 18 2017
STATUS
approved